PROJECT 1: Quality of B Cell and Antibody Responses to Natural Dengue Virus Infections (University of California, Berkeley) SUMMARY The four dengue virus serotypes (DENV1-4) cause the most important mosquito-borne viral disease of humans, with ~390 million infections annually and over 3 billion people worldwide at risk of infection. Yet, no treatment is currently approved for use in humans, and the only registered vaccine is problematic. The overall approach of Project 1 is to take advantage of unique Nicaraguan sample sets to address complex questions about DENV antibody and B cell immunology in a relevant clinical and epidemiological context. The Project is designed to analyze the antibody/B cell immune profile in relation to infection outcome, disease severity, and antibody dynamics. Each aim also addresses specific fundamental questions in dengue immunology. The overall hypothesis of this project is that the quality of B cell and antibody responses, as detemined by the repertoire and characteristics of the antibodies and B cells, impacts outcome of subsequent DENV infection as well as the long-term antibody response. The focus is on characterizing the repertoire and dynamics of the antibody response before and after primary and secondary infections in more detail as new state-of-the-art tools become available in our P01 program. Each aim derives from findings and reagents arising from the current P01. Importantly, we integrate classical state-of-the-art molecular genetics and systems serology approaches to comprehensively examine both antigen-specific and Fc characteristics and effector functions that predict protection or pathogenesis with unprecedented resolution. The proposed research is possible due to the ongoing Pediatric Dengue Cohort Study (2004-present), a community-based prospective cohort study in Managua, Nicaragua, following ~3,700 children, now in its 15th year, and the Dengue Hospital-based Study (2005-present) in Managua, which together enable investigation of pre-infection samples, documented repeat DENV infections, and long-term B cell/antibody responses. This project is highly synergistic with the other Projects in this P01 by sharing similar samples (Projects 3 & 4) and methods and reagents (Project 2) and integrating computational biological analyses and statistical models (Core B) of the B cell/antibody response during DENV natural infections with the T cell response to DENV (Project 3) and with the immune response obtained after live attenuated DENV vaccination (Project 2). Project 1 Aim 1 will define the complete repertoire of type-specific antibodies in dengue-endemic populations in Asia and the Americas, define the footprint of major antigenic sites, and investigate the effect of genotype on epitope recognition in polyclonal sera. Aim 2 will determine predictors of clinical outcome in terms of antibody repertoire and Fc effector function, in relation to inapparent vs. symptomatic infection as well as mild vs. severe dengue disease. Aim 3 will examine epidemiological, antigen-specific, and Fc effector-driven predictors of antibody magnitude and kinetics after primary and secondary DENV infection and will compare the two. This discovery approach willl yield mechanistic insights into immune function. Overall, this project will identify antibody/B cell correlates of protection and pathogenesis, as well as of magnitude and durability of the antibody response, which should be useful for development and evaluation of dengue vaccines.